1. Field of the Invention
The invention relates to a nail for fixing the position and shape of broken long bones.
2. Description of the Related Art
Up until now, relatively large steel nails having a predominantly U-shaped or V-shaped cross section have been used for internally stabilizing broken long bones. The nails stabilize the bones according to the principle of providing support at three points, namely at the beginning, at the end and in the mid-section of the nail. In order to position such nails, large passages matching the diameter of the implanted nail must be cut through the surface of the bone and then through the medullary cavity of the bone. This has the disadvantage that almost all of the medullary cavity has to be reamed out in order to produce such a passage, and as a result in particular the blood supply of the bone is impaired. In addition, because of the three-point support, the force is transmitted via a relatively small area, and to ensure rotational stability it is necessary to use additional mechanisms such as locking screws and the like.
Removing the intramedullary nail after the bone has healed is also a procedure requiring a relatively high degree of effort. The nail is wedged in the medullary cavity and must be knocked out of the cavity using special tools and applying a relatively large amount of force. Again, considerable damage may be sustained by the medullary cavity in the process.
From DE-C-32 01 056 an intramedullary nail is known, in which the shank consists of a hollow body made of a memory alloy which can assume two possible shapes, as a function of temperature. Thus, when in situ, the intramedullary nail can be transformed from having a small cross section to having an expanded cross section, and vice versa. The disadvantage of this prior art type of intramedullary nail is that the application of heat required to expand the diameter of the shank of the nail also causes thermal stress in the bone and the bone marrow.
A nail according to the preamble of claim 1 is known from U.S. Pat. No. 5,102,413. In this known nail a single expandable bladder surrounds fully the main body of the nail.